1. Field of the Invention
The present invention relates to a page description data processing apparatus, a page description data processing method, and a recording medium for performing a particular processing sequence on page description data having a certain attribute, among page description data described by a page description language (PDL), thereby to convert the page description data into more robust page description data (hereinafter referred to as “robustized page description data”).
2. Description of the Related Art
In recent years, DTP processes for setting characters and images generated by the operator with a computer into an electronic page using DTP (DeskTop Publishing) application software installed in the computer have been widely used in the printing and platemaking fields.
The DTP application software generates page description data which express images of respective pages based on elements such as characters and images edited by the operator.
The page description data are vector data independent of the resolution of an output machine such as a printer, a platesetter, or the like, and cannot be output per se from the output machine. Therefore, the page description data are rasterized by a RIP (Raster Image Processor) into raster image data comprising a cluster of dots representative of elements such as characters and images in pages.
When the raster image data are supplied to the output machine such as a printer, a platesetter, or the like, the output machine outputs a hard copy or a printing plate carrying an image based on the raster image data (see Japanese Laid-Open Patent Publication No. 2005-070957).
Generally, according to a page description language, process colors are designated as a set of four colors C, M, Y, K. For example, when an object in cyan C 30% is plotted against a background image in magenta M 50%, the object plotting area in cyan C 30% (C=30%, M=0%, Y=0%, K=0%) is expected to have a color tone of M 50%+C 30%.
According to a page description language such as PDF (Portable Document File), a nonzero overprint mode (overprint mode=(1)) (PDF Reference, 2nd edition, Adobe Portable Document Format Version 1.3, 1st edition, 5th print, published Nov. 20, 2008, Author: Adobe Systems, Publisher: Pearson Education, ISBN4-89471-338-1, pages 171 through 173, 108, 185, etc.) is designated to cause the object plotting area in cyan C 30% to have a color tone of M 50%+C 30% and also to cause the background image in M, Y, K to become the background image in magenta M 50%.
Specifically, in the nonzero overprint mode, when the process colors for the background image are designated as (C=0%, M=50%, Y=0%, K=0%) and the process colors for the object are designated as (C=30%, M=0%, Y=0%, K=0%), the object plotting area has a color tone of M 50%+C 30%, and the background image except the object plotting area has a color tone of M 50% as the process colors M=0%, Y=0%, K=0% for the object are handled as “transparent”.
As defined in “PDF Reference, 2nd edition, Adobe Portable Document Format Version 1.3” referred to above, the nonzero overprint mode (overprint mode=(1)) is not applicable when the object is a shading object in smoothly varying process colors.
However, the market has seen an RIP for producing an overprint of a shading object in process colors in the nonzero overprint mode. If a hard copy or a print is output using such an RIP, then it is different from a hard copy or a print which is output from a normal RIP that does not plot an overprint of a shading object in process colors in the nonzero overprint mode.